Field of the Invention
The present invention relates to an optical system and an imaging apparatus including the same. The optical system is suitable for imaging apparatuses, such as a digital still camera, a video camera, a security camera, and a broadcast camera, including imaging devices; and imaging apparatuses such as a silver-halide camera.
Description of the Related Art
Known focusing methods widely employed in imaging lens systems include an inner focus method and a rear focus method in each of which a lens provided at a position on the image side with respect to a lens provided at the extreme end on the object side is moved for focusing.
Herein, a focusing method in which a lens provided on the image side with respect to an aperture stop is moved for focusing is referred to as the “rear focus method”, and a focusing method in which a lens provided on the object side with respect to the aperture stop is moved for focusing is referred to as the “inner focus method”.
In an imaging lens system employing the inner focus method or the rear focus method, since a relatively small lens is moved for focusing, a quick focusing action is realized.
On the other hand, a macro lens system is known as an imaging lens system intended mainly for short-range imaging with a substantially 1× magnification. An optical system forming the macro lens system is desired to exhibit high optical performance in short-range imaging.
In an imaging lens system disclosed by Japanese Patent Application Laid-Open No. 2012-123340, a plurality of modes are switched there among for different ranges of object distances. The imaging lens system disclosed by Japanese Patent Application Laid-Open No. 2012-123340 is operable in a first mode intended for focusing within a range of object distances from infinity to a first short distance, and in a second mode intended for focusing within a range of object distances from a second short distance that is shorter than infinity to a third short distance that is shorter than the first short distance. In this imaging lens system, the first mode and the second mode are used selectively, whereby the range of object distances that are usable for focusing is widened.
When the mode of the imaging lens system is changed from the first mode to the second mode, the entirety of the imaging lens system is moved toward the object side, whereby the length of the imaging lens system as a whole in the first mode is reduced.
In the optical system disclosed by Japanese Patent Application Laid-Open No. 2012-123340, since the lateral magnification of a focusing lens unit is low, focus sensitivity is too low. Such a configuration increases the length of travel of the focusing lens unit during focusing, leading to a possible increase in the size of the optical system as a whole.